1. Field of the Invention:
The present invention relates to apparatus for controlling a machine tool, and, more particularly, a programmable feed control apparatus for digitally controlling the feed movement of a machine tool.
2. Description of the Prior Art:
In the conventional programmable feed control apparatus, a set of timing pulses is not utilized to read out the control data for the control of the feed movement of a machine tool. Therefore, in order to increase versatility, the component parts of the circuit construction have to be increased in number which results in complicated circuit construction.
Furthermore, in the conventional programmable feed control apparatus, in a normal feed control cycle, the feed amount of the machine member commanded by the control data is preset in a feed control counter. The preset value is subtracted by feed pulses generated from a feed pulse generating circuit into a drive circuit of a servo motor for moving the machine member. When the content of the feed control counter becomes zero, generation of the feed pulses is stopped. When a return command is generated for returning the machine member to a starting position, the feed pulses distributed to the drive circuit are added to or subtracted from the counted value of a return control counter for counting an accumulative moving amount of the machine member from the starting position in response to the moving direction of the machine member. The feed pulses are applied to the drive circuit until the counted value becomes zero. With this construction, a change-over of the counters is necessary either under the normal feed control cycle or at the generation of the return command which results in complicated circuit construction.